This project develops new statistical methods for epidemiology with broad applications and also methods as needed for ongoing projects in epidemiology, particularly those related to reproductive studies. The work this year involved two main projects. (1) Measurements of xenobiotic exposures are often based on levels assayed in blood or urine and the values often fall below the limit of detection of the assay. Good methods for including those censored observations have not been available. We showed that methods developed for survival analysis can be employed and permit confounder adjustment. We illustrated use of our proposed method by applying it to a study of toxic effects on childhood cognitive development in eastern Europe. (2) A second project is extending that method to enable analyses of mixtures of chemicals, making use of existing toxic equivalency factors to create a censored toxicity-weighted average for analysis. We have applied these approache to data from the National Health and Nutrition Examination Survey data relating toxic analytes in blood to the presence of a biomarker, anti-nuclear antibodies, for autoimmunity. In another project we are developing improved methods for adjusting for creatinine levels for studying exposures based on urinary levels or adjusting for serum lipid levels when studying lipophilic chemical analytes in serum. Adjustment for errors in exposure assessment secondary to the diluteness of the urine or secondary to the lipid content of the blood can prevent bias in estimation of effects of environmental exposures and can improve statistical power to identify effects of environmental exposures.